Pitch control in paper making with xylene sulfonic acid-formaldehyde condensates



United States Patent This invention relates to a method of controlling the pitch which occurs in pulp and paper making processes.

One of the frequently occurring problems in paper manufacture is caused by pitch, viz., the coagulation of resinous materials and gums on pulp handling equipment or paper machine parts. This pitch is liberated from the pulp during the screening, beating, and refining processes and tends to accumulate as a colloidal suspension of negatively charged particles. These particles cause trouble by collecting on mill equipment, by filling in the Wires of paper machines thereby producing holes in the finished paper, or by collecting on the felt or machine parts as sticky, dark colored lumps. Troublesome pitch comes mostly from resins or rosinous matter in the fibers themselves. Once pitch becomes attached to the machine parts, the only way it can be removed is by scrubbing with gasoline, kerosene or special cleaning compounds' In some paper mills, special solvents are sprayed on the return side of the wire and on the felt return to remove pitch. All of these methods have proven costly and have not destroyed the formation of pitch during the pulp and paper making process.

In the past, it has been found that the best way to remove pitch is to prevent its formation during the paper making or pulping processes. In the pulping process, this has been accomplished by adding various chemical dispersing agents or surface active agents to the pulp just ahead of the knotter screen headbox. In the paper making process, the dispersing agents are normally added at the beater or prior to the refining operation. These agents have produced a material reduction of the pitch that collects on the paper felt and machine parts during the pulp and paper making operation. This has resulted in very little shut down time in the operation of paper machines and in a decided improvement in screening conditions and pulp cleanliness as well as an improved quality pulp.

One of the most effective and most commonly used dispersing agents in pulp manufacture for getting rid of troublesome pitch are the napthalene sulfonic acid-formaldehyde condensates such as those disclosed by Dr. Poschmann in Pulp and Paper Magazine of Canada 60: T. l09- 114 (1959). While the use of napthalene sulfonic acidformaldehyde condensates in paper manufacture has proven to be an elfective, low cost method of dispersing pitch in many mills, there are many pulp and paper making operations carried out Where even' excessive amounts of the known pitch dispersants have failed to control pitch formation.

, It is an object of this invention to provide an improved method of dispersing pitch formed during the process of pulp and paper making.

It is a further object of this invention to provide a more effective dispersing agent for preventing pitch from collecting on paper felt, wires and other machine parts during the pulping and paper making process.

It is a further object of this invention to provide an improved method of making paper pulp whereby improved cleanliness in the mill equipment and inthe pulp itself is achieved.

Other objects of the invention will be obvious and will in part appear hereinafter.

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I have discovered that by utilizing xylene sulfonic acidformaldehyde condensates and salts thereof as pitch dispersants in paper making and particularly in the sulfate method of pulping, the amount of pitch dispersed during the normal paper making process is quantitively superior to the amount dispersed by any of the known pitch dispersants particularly the naphthalene-sulfonic acid-formaldehyde condensates and their salts. Another advantage achieved by utilizing the pitch dispersants of this invention in a paper making process is that the amount of pitch accumulated on the wires of a paper machine or on parts of machines used in the paper making process is substantially reduced when compared with the amount which accumulates when using the known dispersing agents such as the napthalene sulfonic acid-formaldehyde condensates and their salts. This results in a marked reduction in the shut down time in the paper making operation and a decided improvement in screening conditions and pulp cleanliness as well as an improved quality pulp.

As indicated above, the greatest importance of the new method lies in the possibility of eliminating the difiiculties caused by pitch in the production of paper, above all in the operation of the paper machines. For most purposes, the xylene-sulfonic acid-formaldehyde condensate should be added in the paper making process in amounts of from about 0.05% to about 5.0% based on the weight of the dry pulp added to etiectively reduce the amount of troublesome pitch during a paper making operation. The xylene-sulfonic acid-formaldehyde condensates may be added in greater amounts than 5.0% without detracting from any of their beneficial properties as pitch dispersants. Since no additional beneficial results in the pitch dispersing properties were noticed in concentrations of above 5%, it would seem to be impractical and uneconomic-a1 to utilize larger amounts. The xylene-sulfonic acid-formaldehyde condensates may be added to the system in the form of a dry powder, or as a water solution.

The preferred pitch dispersant for use in the process of paper making is the sodium salt of xylene-sulfonic acidforrnaldehyde condensate. Other salts may be used in this process such as the potassium, calcium, lithium, magnesium, zinc as well as any of the other known salts of sulfonic acid. 7.

Generally the pitch control agent is added to the pulp prior to the screening or refining operation so that it may be mixed with the'pulp for a period of from about 30 to about 60 minutes to obtain the maximum dispersing eifect.

The efficacy of the pitch dispersants of the present invention was completely demonstrated on a full plant scale in several successive pulping and paper making operations. First, a 7 /2 water solution of the sodium salt of xylene sulfonic acid-formaldehyde condensate was fed into groundwood pulp at the rate of six pounds per ton of dry pulp. The introduction of the pitch dispersant into the groundwood pulp was made at the knotter' screens after the mechanical pulping operation. Data obtained from mill records established that during test periods of six days after continued use of the novel pitch dispersant of this in vention, that when the groundwood deckers were cleaned after every six hour period, there was no build up of pitch on the groundwood deckers. In addition there was no build up of pitch on the Fourdrinier wires during the test period. On the other hand, mill tests utilizing naphthalene sulfonic acid-formaldehyde condensates at the same rate instead of the pitch dispersant of this invention showed that the amount of pitch dispersed on Fourdrinier wires of the machine and at the groundwood deckers was considerably greater. This is attributable to the markedly improved pitch dispersing properties of the xylene sulfonic acid-formaldehyde condensates which produced markedly improved screening conditions. In addition, an improved quality pulp was produced by utilizing the pitch dispersant of this invention in the above process. Furthermore, although the actual consumption of chlorine in the bleaching operations carried out in above operation had not been noticeably reduced, there was a noticeable increase in the brightness of the pulp when compared with equivalent amounts of bleaching agent used in connection with a naphthalene sulfonic acid condensate. As a result of better screening conditions in the above m-ill test utilizing the sodium salt of the xylene-sulfonic acid-formaldehyde condensate, the pulp was cleaner and tailings and rejects were lowered.

In a paper mill which produces light weight, heavily refined papers, utilizing predominately a high resin content sulfate pulp as its basic fiber, pitch accumulating on the refining equipment, the Fourdrinier wires and the walls has proven particularly troublesome. It has been found that utilizing various pitch dispersing agents such as the napthalene sulfonic acid-formaldehyde condensate type resins, gave good pitch control but that not less than 20 lbs. of this dispersant per ton of dry pulp was needed to give adequate pitch dispersion. It was shown in an extended mill evaluation that the material of this invention controlled the pitch adequately at one-half the above rate. At this rate of application, no pitch appeared on the paper machine parts or on the beating and refining equipment. Cutting back the rate of napthalene sulfonic acid-formaldehyde condensate caused pitch to build up at these points.

The improved dispersing action provided by the xylene sulfonic acid-formaldehyde condensate makes it useful as a dispersing agent in recovering tall oil by the method disclosed by Sadler in US. Patent 2,802,845, from the sulphate soap skimmings produced in the paper making process. It has been found by utilizing the xylene sulfonic acid-formaldehyde condensates in the separation of tall oil from spent acid and lignin, higher yields and greater purity of tall oil were obtained than by using napthalene sulfonic acid-formaldehyde condensates. The xylene sulfonic acid formaldehyde also provided improved retardation of the agglomeration of lignin, thus reducing time consuming clean-up periods.

The utilization of the dispersing agents of this invention in pulp slurries and tall oil soap solutions should be such that the addition is made prior to the point where the dispersing action is needed and with suflicient retention time (usually 30 minutes to 1 hour or longer) so that the dispersing agent is completely admixed with the slurry for optimum effects. This can be accomplished in the pulping process by adding the agent so that it is mixed in the stock chest or other mixing points in the system prior to the screening operation. In paper making systems the addition point should be early in the wet end system prior to the beating and refining operations. In the tall oil recovery system disclosed by Sadler in U.S. Patent 2,802,845 the addition point should be prior to the centrifuging operation.

The xylene sulfonic acid-formaldehyde condensates and their salts may be prepared by sulfonating xylene with excess sulfuric acid and thereafter condensing the resulting xylene sulfonic acid with formaldehyde. The condensate may then be neutralized with a base, e.g., sodium hydroxide and the product, if desired, may then be treated to remove or reduce the water content, for instance, by spray drying.

The formation of the desired xylene sulfonic acid which can later be utilized by condensing with formaldehyde to produce the pitch dispersant of the invention is accomplished by heating at elevated temperatures at least one mole of sulfonic acid per mole of xylene so as to produce the desired sulfonation. Generally it is impractical to utilize above 5 moles of sulphuric acid per mole of xylene since the unreacted sulfuric acid may dilute the effectiveness of the final product. Sulfonation may be carried out in the presence of an inert organic solvent such as VM&P naphtha. In this manner, water formed during sulfonation may be removed by azeotropic distillation. For best results sulfonation should be carried out at temperatures of above 50 C. and below 150 C. Temperatures above 150 C. may be utilized, but generally it is impractical and uneconomical .to use such high temperatures. Any conventional procedure for sulfonating xylene may be utilized to produce xylene sulfonic acid.

In the condensation of xylene sulfonic acid and formaldehyde, temperatures of from about 75 to 115 C. and reaction times of about 30 minutes to 20 hours or more may be utilized. In this reaction, formaldehyde, paraformaldehyde, trioxane or any material liberating formaldehyde may be used. As a matter of convenience, a 37% by weight aqueous solution of formaldehyde may be used, since it is available commercially. The amount of formaldehyde utilized in the condensation reaction may vary from 0.2 to 1.5 moles of formaldehyde per mole of xylene sulfonic acid.

The neutralization of the condensate may be accomplished by introducing either as a solid or as an aqueous solution, a neutralizing agent. Any base or basic salt which forms a sulfonic acid salt may be used as a neutralizing agent. The base may be added together with the condensate in the sulphite mill or paper mill so as to form the salt directly in the mill. Alternatively, it may be convenient to form the salt by adding the base directly to the condensate before addition to the paper mill or sulphite mill. Typical neutralizing agents include sodium hydroxide, potassium hydroxide, calcium hydroxide, barium hydroxide, as Well as zinc, lithium and magnesium hydroxides. The amount of neutralizing agent should preferably be approximately the stoichiometric amount required to neutralize the sulfonic acid condensate as well as unreacted sulfuric acid since a large excess thereof will result in an impure product. The neutralizing agent may also be supplied in a stoichiometric deficiency. The neutralized product may be utilized in the paper mill in the form of an aqueous solution or the amount of water may be reduced or the water may be removed entirely by spray drum or tray drying.

The following examples further illustrate the present invention, however, they are not to be construed in a limiting sense.

EXAMPLE I 212 grams of xylene (2 moles) were placed in a flask. Then 294 grams of concentrated sulfuric acid (3 moles) was slowly added to the flask and the temperature rose to C. After all of the sulfuric acid was added, the temperature was held at 80 C. to C. for one hour. After this period 75 grams of water and 110 grams of 37% formaldehyde (1.35 moles) were added under constant stirring to the flask and the temperature rose in the flask to about C. When all of the water and formaldehyde were added the temperature of the flask was maintained at 110 C. for five hours. After this period, there was no noticeable smell of formaldehyde and the flask was cooled to room temperature. Next 320 grams of 50% aqueous sodium hydroxide solution (4 moles) and grams of water were added to the flask so as to produce the sodium salt of xylene sulfonic acidformaldehyde condensate which was a dark red viscous liquid. This product was then spray dried to remove the water.

EXAMPLE II 106 grams of xylene (1 mole) was placed in a flask. Then 245 grams of concentrated sulfuric acid (2.5 moles) was added slowly to the flask and the temperature rose to about 50 C. During the addition, the flask was cooled so as to maintain a temperature of 50 C. After all of the sulfuric acid was added, the temperature was held at 50 C. for 20 minutes. After this period 75 grams of water and 82 grams of a 37% formaldehyde solution were slowly added under constant stirring to ar-a E e) the flask and the temperature rose in the flask to about 80 C. When all of the Water and formaldehyde were added, the temperature of the flask was maintained at 80 C. for two hours. After this period, it was observed that there was no noticeable smell of formaldehyde and the flask was cooled to room temperature. Then 200 grams of an aqueous 50% sodium hydroxide solution (2% moles) and 100 grams of water were added to the flask so as to produce the sodium salt of xylene sulfonic acid-formaldehyde condensate which was a dark red viscons liquid. This product was then tray dried at room temperature for two days to remove the water.

EXAMPLE III In this example, the prior art dispersant, viz., the condensate of naphthalene sulfonic acid-formaldehyde was prepared utilizing the proportions of Example I above.

256 grams of naphthalene (2 moles) was placed in a flask. Then 294 grams of concentrated sulfuric acid (3 moles) was slowly added to the flask and the temperature rose to 80 C. After all of the sulfuric acid was added, the temperature was held at 80 to 85 C. for one hour. After this period 75 grams of water and 110 grams of 37% formaldehyde (1.35 moles) were added under constant stirring to the flask and the temperature rose in the flask to about 90 C. When all of the water and formaldehyde were added, the temperature of the flask was maintained at 110 C. for five hours. After this period, there was no noticeable smell of formaldehyde and the flask was cooled to room temperature. Next 320 grams of 50% aqueous sodium hydroxide solution (4 moles) and 100 grams of water were added to the flask so as to produce the sodium salt of naphthalene sulfonic acid-formaldehyde condensate which was a dark red viscous liquid. This product was then spray dried to remove the water.

EXAMPLE IV The following test was performed to determine the relative pitch dispersing properties of the compounds produced by Examples I, II and III.

15 grams of shredded alpha cellulose pulp (produced by the soda pulping process) was placed in a tank containing 500 cc. of water. 15 grams of pitch, which in this case was the sap from the Balsam Fir tree, was also added to the tank. Separate runs were made, each using 0.15 gram of one of the dispersants prepared in Examples I, II and III. In each of the runs, the mixture was agitated at 180 F. by a mechanical agitator for 2 hours which was weighed before use. After agitation was finished, the agitator was removed and dried in an oven at 100 C. for 30 minutes and the increase in weight determined. This represented the amount of undispersed pitch which collected on the agitator. A blank run was made wherein no dispersant was used. The percent pitch for each run including the blank was calculated as Increase in Weight of agitator Weight of known pitch added The results for each determination are tabulated below.

Table I Example II 18.9 6

Example I 15.2

As seen from the above table, utilizing xylene sulfonic acid-formaldehyde condensate in place of naphthalene sulfonic acid-formaldehyde condensate reduces the amount of pitch deposited on the agitator by almost half. Hence it is seen that xylene sulfonic acid-formaldehyde condensate is a far superior pitch dispersing agent than known pitch dispersing agents such as naphthalene sulfonic acid-formaldehyde condensate.

My dispersants can also be utilized with the same beneficial results with either bleached or unbleached pulp produced from the groundwood (mechanical pulping), semi chemical, chemi-groundwood, sulfite, sulfate (kraft), or cold soda pulping processes. My dispersants may be utilized to disperse pitch in the making of pulp as well as in the subsequent paper making steps. However, it is understood that my invention is not limited to any specific process of making pulp or paper but is useful wherever the problem of pitch arises in paper making and pulping.

Having described my invention what I claim is new and desire to secure by Letters Patent is:

1. In pulp and paper making processes, a method of preventing deposition of pitch from pulp which comprises adding to the pulp a material selected from the group consisting of xylene sulfonic acid-formaldehyde condensates and their basic salts in the amount of from about 0.05% to about 5 calculated on the weight of dry pulp.

2. In pulp and paper making processes, a method of preventing deposition of pitch from pulp which comprises adding to the pulp the sodium salt of xylene sulfonic acid-formaldehyde condensate, said salt being added in an amount of from about 0.05 to about 5%, calculated on the weight of the dry pulp.

3. In the pulping of wood, the improvement which comprises adding to the pulp a material selected from the group consisting of xylene sulfonic acid-formaldehyde condensate and its basic salts and thereafter screening said pulp, said screening taking place at least 30 minutes after said material is added to the pulp, said salt being added in an amount of from about 0.05% to about 5 calculated on the weight of the dry pulp.

4. The process of claim 3 wherein said material is the sodium salt of xylene sulfonic acid-formaldehyde condensate.

5. In pulp and paper making processes, a method of preventing deposition of pitch from alpha cellulose pulp comprising the step of adding to alpha cellulose pulp, a material selected from the group consisting of xylene sulfonic acid-formaldehyde condensates and their basic salts in an amount of from about 0.05 to about 5%, calculated on the weight of dry pulp.

References Cited in the file of this patent UNITED STATES PATENTS 1,534,019 Baddiley et al. April 21, 1925 1,696,199 Gunther et al. Dec. 25, 1928 1,758,277. Daimlet et al. May 13, 1930 FOREIGN PATENTS 596,498 Canada April 19, 1960 OTHER REFERENCES Lenher: Textile Cororist, April 1941, pp. 265-267,

5 Use of Wetting Agents.

Casey: Pulp and Paper, 2nd edition, vol. 2, Interscience Publishers, 1960, page 1096.

*8 BALL a Attest:

ERNEST W. S 5 il Attesting Officer ulfonjidTread f f NR Commissioner of Patents I JNITED STATES PATENT OFFICE CER'I'IFHLX'IE OF CORRECTION Patent No. 3,154,466 October 27, 1964 William M. Nothum Column 3, line 69, for "sulfonic" read sulfuric -n Signed and sealed this 8th clay of March 1966.

ERNEST W. SWIDER EDWARD -J. BRENNER Attesting Officer Commissioner of Patents 

1. IN PULP AND PAPER MAKING PROCESSES, A METHOD OF PREVENTING DEPOSITION OF PITCH FROM PULP WHICH COMPRISES ADDING TO THE PULP A MATERIAL SELECTED FROM THE GROUP CONSISTING OF XYLENE SULFONIC ACID-FORMALDEHYDE CONSENDATES AND THEIR BASIC SALTS IN THE AMOUNT OF FROM ABOUT 0.05% TO ABOUT 5%, CALCULATED ON THE WEIGHT OF DRY PULP. 